1. Field of the Invention
The present invention relates to a photoelectric converting device, and more particularly to a photoelectric converting device composed of plural line sensors.
2. Related Background Art
Line sensors are already used in information processing apparatus such as a facsimile apparatus, and are composed for example of charge coupled devices (CCD).
An example of the CCD line sensor is shown in FIG. 17.
In a CCD sensor as shown in FIG. 17, signals from a sensor unit 1 are transferred by transfer gates 2 to two analog shift registers 3 provided respectively for even and odd pixels, then further transferred by said analog shift registers 3 and again aligned as sequential signals in an output gate 4. The signals are then amplified by a preamplifier 5 and released to the outside. The analog shift registers 3 and the transfer gates 2 are controlled by a drive pulse circuit 6.
Recent advances in image processing apparatus capable of handling color images have stimulated the demand for an image reader for color original images, and for this purpose there is employed a color image reader equipped with three parallel line sensors for respectively obtaining signals of red, green and blue.
If such a color line sensor is composed simply of the CCD line sensors of the above-explained structure, there is required a large chip since there are required large areas between the light-receiving portions.
The color line sensor is usually composed of plural line sensors for different colors, each of which is composed of a light-receiving area constituting the photoelectric conversion area, and an output area shielded from light and provided with scanning circuits, output wirings etc. When such a color line sensor is used in reading an original image, the signals of red (R), green (G) and blue (B) cannot be obtained at the same time because of the positional difference in the light-receiving areas of the line sensors of different colors, so that the signals from different line sensors have to be temporarily stored in a memory for matching the timing of signals of different colors. For reducing the cost of an image processing apparatus utilizing a color line sensor, it is desirable to reduce the number of such memories, but the output area between light-receiving areas (said output area being hereinafter called line space) must be shielded from light for reducing the number of memories.
In the following there will be explained the problems associated with the reduction in the line space, in relation to a photoelectric converting device disclosed by the assignee of the present application in Japanese Patent Application Sho 62-6252.
FIG. 18 is a cross-sectional view of a photoelectric conversion cell of the known photoelectric converting device.
On an n-type silicon substrate 101 there is formed, by epitaxial growth, an n.sup.- -layer 102 constituting a collector area, in which formed are a p-base area 103 and an n.sup.+ -emitter area 104 to constitute a bipolar transistor. In said n.sup.- -layer 102 there are further formed p.sup.+ -areas 105, 106 constituting drain and source areas of a p-channel MOS transistor, and a gate electrode 108 is formed across an oxide film. A transparent insulating layer 109 is formed thereon, and a drain electrode 110 and an emitter electrode 111 are formed through contact holes. There are further provided a transparent insulating layer 112 and a light shielding layer 113.
When the base area 103 is irradiated with light, carriers (holes in this case) are accumulated corresponding to the quantity of incident light, and an output signal corresponding to the amount of said carriers is read from the emitter electrode 111. The carriers accumulated in the base area 103 are released from the source area 106, by turning on the p-channel MOS transistor.
The base area 103 shown in FIG. 18 is larger than the drain/source areas 105, 106 and the emitter area 104 of the p-channel MOS transistor, but the areas of the drain/source areas 105, 106 and of the emitter area 104 are not negligible since the pitch (distance between adjacent pixels) of pixels becomes small in a line sensor with an elevated number of pixels.
In a line sensor containing only one array of pixels, the space is not a problem since it is only required to secure the apertures of the base areas of a single line, but, in a multi-line sensor containing plural arrays of pixels, the line space becomes inevitably wide because the above-mentioned drain/source areas 105, 106 and the emitter area 104 have to be formed between the lines.